1. Field of the Invention
The present invention relates to a method of forming visible images in which magnetically attractable toner powder comprising resin particles containing magnetically attractable material is introduced to an image forming zone between an image registration medium and a moving conveying medium which exerts a magnetic force of attraction on the toner powder, such that the toner powder is selectively deposited on the image registration medium in the image forming zone by electrostatic attraction in accordance with an image pattern.
2. Discussion Of Related Art
According to a process taught by U.S. Pat. No. 4,154,520, latent electrostatic image patterns on an image registration medium are developed in a copying machine by means of toner powder fed by a magnetic conveying medium in the form of a magnetic brush The circumferential speed of the magnetic brush according to this method should be at least twice that of the speed of conveyance of the image registration medium and preferably three to five times such speed. The reason for this is that at low circumferential speed of the magnetic brush developing problems occur, such as inadequate gradation, deposition of toner particles outside the image patterns, and toner accumulation or over-development These developing problems ultimately lead to poor image quality of the copy.
Although such developing problems can be minimized by the use of a much higher circumferential speed, the higher brush speed is not without problems due to the increased mechanical load placed on both the image registration medium and the toner powder. As a result of the higher mechanical load, fine abrasive dust forms in the powder brush and is thrown from the latter, thus causing soiling of the copying machine. In addition, fine abrasive dust is also permanently deposited on the image registration medium, thus reducing its life.
Thus, in order to ensure proper functioning of the copying machine regular cleaning of the machine is required.